cloudflared-mirror/ingress/icmp_linux.go

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//go:build linux
package ingress
import (
"context"
"fmt"
"net"
"net/netip"
"sync"
"sync/atomic"
"time"
"github.com/google/gopacket/layers"
"github.com/pkg/errors"
"github.com/rs/zerolog"
"golang.org/x/net/icmp"
"github.com/cloudflare/cloudflared/packet"
)
// The request echo ID is rewritten to the port of the socket. The kernel uses the reply echo ID to demultiplex
// We can open a socket for each source so multiple sources requesting the same destination doesn't collide
type icmpProxy struct {
srcToFlowTracker *srcToFlowTracker
listenIP netip.Addr
logger *zerolog.Logger
shutdownC chan struct{}
}
func newICMPProxy(listenIP netip.Addr, logger *zerolog.Logger) (ICMPProxy, error) {
if err := testPermission(listenIP); err != nil {
return nil, err
}
return &icmpProxy{
srcToFlowTracker: newSrcToConnTracker(),
listenIP: listenIP,
logger: logger,
shutdownC: make(chan struct{}),
}, nil
}
func testPermission(listenIP netip.Addr) error {
// Opens a non-privileged ICMP socket. On Linux the group ID of the process needs to be in ping_group_range
// For more information, see https://man7.org/linux/man-pages/man7/icmp.7.html and https://lwn.net/Articles/422330/
conn, err := newICMPConn(listenIP)
if err != nil {
// TODO: TUN-6715 check if cloudflared is in ping_group_range if the check failed. If not log instruction to
// change the group ID
return err
}
// This conn is only to test if cloudflared has permission to open this type of socket
conn.Close()
return nil
}
func (ip *icmpProxy) Request(pk *packet.ICMP, responder packet.FlowResponder) error {
if pk == nil {
return errPacketNil
}
echo, err := getICMPEcho(pk)
if err != nil {
return err
}
return ip.sendICMPEchoRequest(pk, echo, responder)
}
func (ip *icmpProxy) Serve(ctx context.Context) error {
<-ctx.Done()
close(ip.shutdownC)
return ctx.Err()
}
func (ip *icmpProxy) sendICMPEchoRequest(pk *packet.ICMP, echo *icmp.Echo, responder packet.FlowResponder) error {
icmpFlow, ok := ip.srcToFlowTracker.get(pk.Src)
if ok {
return icmpFlow.send(pk)
}
conn, err := newICMPConn(ip.listenIP)
if err != nil {
return err
}
flow := packet.Flow{
Src: pk.Src,
Dst: pk.Dst,
Responder: responder,
}
icmpFlow = newICMPFlow(conn, &flow, uint16(echo.ID), ip.logger)
go func() {
defer ip.srcToFlowTracker.delete(pk.Src)
if err := icmpFlow.serve(ip.shutdownC, defaultCloseAfterIdle); err != nil {
ip.logger.Debug().Err(err).Uint16("flowID", icmpFlow.echoID).Msg("flow terminated")
}
}()
ip.srcToFlowTracker.set(pk.Src, icmpFlow)
return icmpFlow.send(pk)
}
type srcIPFlowID netip.Addr
func (sifd srcIPFlowID) Type() string {
return "srcIP"
}
func (sifd srcIPFlowID) String() string {
return netip.Addr(sifd).String()
}
type srcToFlowTracker struct {
lock sync.RWMutex
// srcIPToConn tracks source IP to ICMP connection
srcToFlow map[netip.Addr]*icmpFlow
}
func newSrcToConnTracker() *srcToFlowTracker {
return &srcToFlowTracker{
srcToFlow: make(map[netip.Addr]*icmpFlow),
}
}
func (sft *srcToFlowTracker) get(srcIP netip.Addr) (*icmpFlow, bool) {
sft.lock.RLock()
defer sft.lock.RUnlock()
flow, ok := sft.srcToFlow[srcIP]
return flow, ok
}
func (sft *srcToFlowTracker) set(srcIP netip.Addr, flow *icmpFlow) {
sft.lock.Lock()
defer sft.lock.Unlock()
sft.srcToFlow[srcIP] = flow
}
func (sft *srcToFlowTracker) delete(srcIP netip.Addr) {
sft.lock.Lock()
defer sft.lock.Unlock()
delete(sft.srcToFlow, srcIP)
}
type icmpFlow struct {
conn *icmp.PacketConn
flow *packet.Flow
echoID uint16
// last active unix time. Unit is seconds
lastActive int64
logger *zerolog.Logger
}
func newICMPFlow(conn *icmp.PacketConn, flow *packet.Flow, echoID uint16, logger *zerolog.Logger) *icmpFlow {
return &icmpFlow{
conn: conn,
flow: flow,
echoID: echoID,
lastActive: time.Now().Unix(),
logger: logger,
}
}
func (f *icmpFlow) serve(shutdownC chan struct{}, closeAfterIdle time.Duration) error {
errC := make(chan error)
go func() {
errC <- f.listenResponse()
}()
checkIdleTicker := time.NewTicker(closeAfterIdle)
defer f.conn.Close()
defer checkIdleTicker.Stop()
for {
select {
case err := <-errC:
return err
case <-shutdownC:
return nil
case <-checkIdleTicker.C:
now := time.Now().Unix()
lastActive := atomic.LoadInt64(&f.lastActive)
if now > lastActive+int64(closeAfterIdle.Seconds()) {
return errFlowInactive
}
}
}
}
func (f *icmpFlow) send(pk *packet.ICMP) error {
f.updateLastActive()
// For IPv4, the pseudoHeader is not used because the checksum is always calculated
var pseudoHeader []byte = nil
serializedMsg, err := pk.Marshal(pseudoHeader)
if err != nil {
return errors.Wrap(err, "Failed to encode ICMP message")
}
// The address needs to be of type UDPAddr when conn is created without priviledge
_, err = f.conn.WriteTo(serializedMsg, &net.UDPAddr{
IP: pk.Dst.AsSlice(),
})
return err
}
func (f *icmpFlow) listenResponse() error {
buf := make([]byte, mtu)
encoder := packet.NewEncoder()
for {
n, src, err := f.conn.ReadFrom(buf)
if err != nil {
return err
}
f.updateLastActive()
if err := f.handleResponse(encoder, src, buf[:n]); err != nil {
f.logger.Err(err).Str("dst", src.String()).Msg("Failed to handle ICMP response")
continue
}
}
}
func (f *icmpFlow) handleResponse(encoder *packet.Encoder, from net.Addr, rawPacket []byte) error {
// TODO: TUN-6654 Check for IPv6
msg, err := icmp.ParseMessage(int(layers.IPProtocolICMPv4), rawPacket)
if err != nil {
return err
}
echo, ok := msg.Body.(*icmp.Echo)
if !ok {
return fmt.Errorf("received unexpected icmp type %s from non-privileged ICMP socket", msg.Type)
}
addrPort, err := netip.ParseAddrPort(from.String())
if err != nil {
return err
}
icmpPacket := packet.ICMP{
IP: &packet.IP{
Src: addrPort.Addr(),
Dst: f.flow.Src,
Protocol: layers.IPProtocol(msg.Type.Protocol()),
},
Message: &icmp.Message{
Type: msg.Type,
Code: msg.Code,
Body: &icmp.Echo{
ID: int(f.echoID),
Seq: echo.Seq,
Data: echo.Data,
},
},
}
serializedPacket, err := encoder.Encode(&icmpPacket)
if err != nil {
return errors.Wrap(err, "Failed to encode ICMP message")
}
if err := f.flow.Responder.SendPacket(serializedPacket); err != nil {
return errors.Wrap(err, "Failed to send packet to the edge")
}
return nil
}
func (f *icmpFlow) updateLastActive() {
atomic.StoreInt64(&f.lastActive, time.Now().Unix())
}